bV It. GREIG-SMITH. 313 



weighing 30 drops discharged from the pipette while held verti- 

 cally. Three weighings were made, and as these never varied 

 from a milligram or two, the weight of an average droplet was 

 obtained. The volume of water necessary to make about lOc.c. 

 of the required dilution was pipetted into a wide-mouthed ounce 

 bottle, and the requisite number of drops of oil were added. The 

 bottle was corked and shaken 300 times at intervals and finally 

 before the abstraction of 2 e.c. This quantity was pipetted into 

 a small tube, 5 x § inches, a drop* of a 20 hours' broth culture 

 of B. coli communis was added, and the tube was put into a 

 water-bath at 20° for the allotted time. 



At certain intervals the dilutions were shaken and a small 

 quantity withdrawn from each by means of a platinum spiral,! 

 and put into a test tube containing 3 c.c. of Lemco broth. The 

 infected Lemco tubes were incubated at 37° for two days. 



The dilutions were generally made in steps of 100 up to 1,000, 

 then by 200 up to 2,000. but in certain cases this was departed 

 from and the steps made smaller, as in the case of cineol and 

 phenol. 



When the oils are diluted with water, they are more or less 

 opalescent, depending upon the relative amounts of oil and 

 water. The oil slowly dissolves, and the faintly opalescent 

 dilutions become clear. 



The question arose as to when the dilutions should be tested, 

 that is to say, at what time, after their preparation, were they 

 most potent ? To answer this question, cineol was tested, and 

 it was found to he as effective in twenty minutes as in four 

 hours, but that it became less and less germicidal as the time 

 extended from one to twelve days. This is in keeping with the 

 idea that an emulsion of a disinfectant is more effective than a 

 solution, and, with cineol, the potency seemed to keep pace with 

 thr solubility. Those dilutions which just became bright at 12* 



* From a capillary pipette discharging 40 drops of broth per gram. 

 1 Made by rolling in ordinary platinum needle wire live times round a 

 No.18 wire. It withdrew 7 milligrams pf broth. Several spirals were 

 used, so that one was always cold. They were consistent in picking up 

 the same weight of liquid. 



